1. Field of the Invention
The present invention relates to a method and an apparatus for carrying out image processing on image data obtained by a digital camera. The present invention also relates to a program embodied on a computer-readable recording medium to cause a computer to execute the image processing method.
2. Description of the Related Art
In a digital still camera (hereinafter referred to as a digital camera), an image obtained by photography can be recorded as digital image data in a recording medium such as an internal memory or an IC card, and can be reproduced by a printer or a monitor based on the digital image data. In the case where an image obtained by a digital camera is printed, the image is expected to have as high a quality as a print generated from a negative film.
When a print is generated from such image data, the quality thereof can be improved by carrying out various types of image processing such as density conversion processing, white balance processing, gradation conversion processing, saturation enhancement processing, and sharpness processing on the image data. Consequently, a method for obtaining a higher-quality print has been proposed U.S. Pat. No. 6,011,547. In this method, photography information such as an ON or OFF state of flash and the type of lighting is added as tag information to image data obtained by a digital camera. Appropriate image processing is carried out on the image data with reference to the photography information added to the image data.
In some cases, such tag information includes information useful for image processing, such as a distance to a subject, brightness of the subject, exposure, a photometric quantity at the time of photography, and presence or absence of counterlight, in addition to an ON or OFF state of flash and the type of lighting. For this reason, various methods have also been proposed for image processing to be carried out on image data with reference to photography information (U.S. Pat. Nos. 6,133,983, 5,739,924, 5,016,039, 5,596,387, 5,710,948, and Japanese Unexamined Patent Publication Nos. 8(1996)-307767, 11(1999)-88576, for example).
Furthermore, as methods of carrying out tone processing on image data, various methods have also been proposed for calculating a tone processing condition used in gradation conversion according to a histogram of image data (Japanese Unexamined Patent Publication No. 9(1997)-200531, and U.S. Pat. No. 5,812,286, for example). Moreover, another method of calculating a tone processing condition has also been proposed (Japanese Unexamined Patent Publication No. 2000-196890) so as to cause density of a main subject such as a human face included in an image to be kept in a target density range while keeping the highest density value and the lowest density value in the image as they are.
In such image processing methods described above, image processing is carried out on image data with use of photography information. However, in the case where a main subject in an image represented by the image data varies from people to scenery for example, the appropriate image processing condition cannot be found with accuracy if the photography information is used alone.
In the methods of finding the tone processing condition described above, the appropriate tone processing condition is difficult to find in accordance with various scenes such as people and scenery, although the histogram or the information on the density is used in the methods.